1. Field of the Invention
The invention relates to a circuit arrangement having at least two signal paths which can be alternately enabled by feeding respective controllable current sources and by means of logic signals selecting one of these controllable current sources, while, at a transition from one signal path to the other, said controllable current sources of the relevant two signal paths are controllable by means of a time-continuously changing control signal during a transition interval, such that currents which can be supplied by these two controllable current sources change continuously and in opposite directions.
2. Description of the Related Art
DE-OS 32 00 071 discloses a signal transmission device with a stepwise adjustable transfer characteristic, comprising at least a group of controllable switches for applying a signal from different inputs to an output. The device comprises control means with which, each time, one of these switches is rendered conducting, and with which these switches can be rendered conducting and non-conducting by means of a control signal. The device also comprises a control signal generator for generating a first control signal uniformly changing as a function of time, with which a given switch from the group of controllable switches is gradually rendered conducting, and for generating a second control signal which is complementary to the first control signal and with which simultaneously another switch from said group of controllable switches is gradually rendered non-conducting.
DE-OS 32 22 607 discloses a circuit arrangement comprising a plurality of signal paths constituted by active circuits. Signals having different levels are supplied from a common output via these signal paths. The signal paths can be enabled by means of a switchable current source. Each current source is constituted by at least an I.sup.2 L gate. These gates are divided into a first group and second group, and the injector terminals of the first group are connected to a first junction point and the injector terminals of the second group are connected to a second junction point. The control inputs of the I.sup.2 L gates are controlled in such a way that, at the transition from one signal path to another, two I.sup.2 L gates associated with one of the signal paths and with one of the groups can convey current at least during a transition phase. The junction points are chosen to be such that the output currents of the two I.sup.2 L gates change continuously and in opposite directions during the transition phase.
In these known circuit arrangements, the transition from one setting position to the next is extended and rounded for a predetermined period of time. This reduces interfering noise occurring during the setting process and caused by operating point offsets, voltage pulses and modulation effects. Particularly, audible signal interferences can be suppressed when this circuit arrangement is used for audio signals.
However, it has been found that a proportionally high number of components is required for a practical implementation of the circuit arrangements described.